Alkaline benzylic ether phenolic resin binders

ABSTRACT

Modified benzylic ether resole resins and process for their preparation. The resins are prepared by treating a phenol with a molar excess of aldehyde in the presence of a divalent metal ion catalyst at a pH below 7 followed by further reaction at a pH above 8 in the presence of an alkaline catalyst. Alkaline solutions of the resins are used as foundry binders in an ester cure process.

FIELD OF THE INVENTION

This invention relates to modified benzylic ether resole resins usefulin binder compositions, moldable compositions which include the bindersand aggregate material, and a process for making moldable compositionsfrom them. More particularly, the invention relates to foundry bindercompositions, moldable compositions including the same and aggregatematerial, and foundry cores for molds made therefore, including aprocess or their manufacture.

BACKGROUND OF THE INVENTION

Binders or binder systems for foundry cores and molds are well known. Inthe foundry art, cores or molds for making metal castings are normallyprepared from a mixture of an aggregate material, such as sand, and abinding amount of a binder or binder system. Typically, after theaggregate material and binder have been mixed, the resulting mixture isrammed, blown or otherwise formed to the desired shape or pattern, andthen cured with the use of catalysts and/or heat to a solid, curedstate.

Resin binders used in the production of foundry molds and cores ar oftencured at high temperatures to achieve the fast-curing cycles required infoundries. However, in recent years, resin binders have been developedwhich cure at low temperatures, to avoid the need for high-temperaturecuring operations which have higher energy requirements and which oftenresult in the production of undesirable fumes.

One group of processes which do not require heating in order to achievecuring of the resin binder are referred to as "cold-box" processes. Insuch processes, the binder components are coated on the aggregatematerial, such as sand, and the material is blown into a box of thedesired shape. Curing of the binder is carried out by passing a gaseouscatalyst or hardener at ambient temperatures through the moldedresin-coated material.

One such "cold-box" process employs an aqueous alkaline solution of aphenolic resole resin as the binder. This binder is cured by passing thevolatile ester through the molded resin-coated material. The process isdescribed in detail in U.S. Pat. No. 4,468,359 (Re. 32,720) which isincorporated herein by reference in its entirety.

The ester cured process is superior to some of the earlier processesfrom an environmental standpoint. However, the tensile strengths of thecores made by this process tend to be somewhat lower than those preparedby other "cold-box" processes.

We have now discovered that certain modified benzylic ether resoleresins, not hitherto used with ester-cured phenolic binder systems,speed the rate of cure of such systems, giving molds and cores withhigher initial tensile strength. This reduces breakage of the cores whenthey are first removed from the core boxes. We have also discovered thatif certain additives are used with these resins they give cores andmolds of even greater tensile strength.

It is known that benzylic ether resins can be prepared by the reactionof an aldehyde with phenol in the presence of a divalent metal ioncatalyst, U.S. Pat. No. 3,485,797. Their use in making polyurethanebinders for foundry cores and molds is well known. More recently, inU.S. Pat. No. 4,668,759, a modified phenolic resole resin was preparedby partial reaction of an aldehyde with phenol under strongly basicconditions followed by further reaction at a pH below 7 in the presenceof a catalyst which promotes formation of benzylic ether bridges. Thepresently-disclosed resins differ from both of the foregoing products.The new resins are prepared by partial reaction of the aldehyde andphenol in the presence of a benzylic ether promoting catalyst and thencompletion of the reaction under alkaline conditions.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided a process forpreparing a modified benzylic ether resole resin comprising the steps:

(a) reacting a phenol with a molar excess of an aldehyde in the presenceof a divalent metal ion catalyst at a pH below 7 until from about 20% toabout 90% by weight of the aldehyde has combined with the phenol;

(b) adding sufficient basic catalyst to the mixture of step (a) to raisethe pH to at least about 8; and

(c) heating the mixture obtained in step (b) until the free aldehyde inthe mixture is less than about 5% by weight of the mixture.

Further, in accordance with this invention, there is provided a modifiedbenzylic ether resole resin obtained by the above process, a foundrymolding composition which comprises a mixture of the modified benzylicether resole resin of this invention with granular refractory material,and a process for the production of foundry cores and molds using thisfoundry molding composition.

DETAILED DESCRIPTION OF THE INVENTION

In the practice of this invention, the modified phenolic resole resinsare produced by a multistep process. In the first step of the process, aphenol reacts with a molar excess of an aldehyde in the presence of adivalent metal ion catalyst. The phenols employed in the formation ofthe phenolic resin are generally any of the monohydric phenols which maybe utilized to prepare phenolic resins. Exemplary phenols include phenolitself and the cresols.

The aldehyde employed in the formation of the phenolic resin may alsovary widely. Suitable aldehydes include any of the aldehydes heretoforeemployed in formation of phenolic resins, such as formaldehyde,acetaldehyde, propionaldehyde, furfuraldehyde, and benzaldehyde. Ingeneral, the aldehydes employed have the formula RCHO, where R is ahydrogen or a hydrocarbon radical of 1 to 8 carbon atoms. The mostpreferred aldehyde is formaldehyde.

The divalent metal ion catalyst is one which causes formation ofortho-ortho benzylic ether bridges between the phenolic nuclei in theresin. Catalysts useful for this purpose include salts of the divalentions of Mn, Zn, Cd, Mg, Co, Ni, Fe, Pb, Ca, and Ba. A preferred catalystis zinc acetate. These catalysts give phenolic resins wherein thebridges joining the phenolic nuclei in the resin are predominantlyortho-ortho benzylic ether bridges of the general formula --CH₂(OCH₂)_(n) -- where n is a small positive integer.

The preferred phenolic resins employed in the practice of this inventionare made from phenol and formaldehyde at a mole ratio of formaldehyde tophenol in the range of from about 1.2:1 to about 2.6:1. The mostpreferred mole ratio of formaldehyde to phenol is a mole ratio in therange of from about 1.5:1 to about 2.2:1.

The first step of the process is carried out by treating the mixture ofphenol and aldehyde in an aqueous solution with the divalent metal ioncatalyst at a temperature sufficient to cause reaction, preferably atabout 70° C. or above until the free aldehyde in the mixture is in thedesired range. Suitable resins are obtained when the first step of theprocess is carried out until from about 20% to about 90% of the aldehydehas reacted with the phenol. Reaction temperatures are controlled byconventional means, such as heating, cooling, or portionwise addition ofcatalyst.

When the reaction has proceeded to the desired stage, as indicated bythe amount of free aldehyde remaining in the reaction mixture, a basiccatalyst is added to the reaction mixture to raise the pH to at leastabout 8. Preferably, the pH of the mixture is at least about 9.

In the next step of the process, the reaction mixture containing thebasic catalyst is heated again at a temperature sufficient to causereaction, preferably at about 55° C. or above. Heating is continueduntil the free aldehyde in the solution is less than about 5%,preferably less than about 2% by weight.

Any of the commonly used basic catalysts may be used to prepare thephenolic resole resin. However, the preferred alkali in the product isKOH when the resin is used in the ester cured process. For this reason,this alkali may be used in the manufacture of this resin or may be addedto the resin subsequent to its preparation. The alkalinity of the resinis expressed in terms of the molar ratio of KOH to the phenol in theresin. However, other alkalis are not excluded and may be used alone orin combination with KOH.

The molar ratio of KOH:phenol in the final resin solution used in theester cured process is in the range of from about 0.2:1 to about 1.2:1,preferably from about 0.4:1 to about 0.9:1.

When the reaction reaches the desired degree of completion, the watercontent of the resin may be adjusted to the desired value. Water contentof the resin may be adjusted by evaporation under reduced pressure or bythe addition of water.

The resins of this invention are useful as binders for preparing foundrymolding compositions. As noted above, they are particularly usefulbinders in the ester cured process. When the resins are used in thisprocess, the solids content of the aqueous alkaline solution ispreferably in the range of from about 40% to about 75% by weight.

Foundry molding compositions used in the ester cured process comprise agranular refractory material and from about 0.5% to about 8% by weightof the refractory material of the aqueous alkaline binder solution. Thegranular refractory materials used in the molding composition may be anyof the refractory materials employed in the foundry industry for theproduction of molds and cores, such as silica sand, chromite sand,zircon sand or olivine sand and mixtures thereof. When such sands areused, it is preferred that the binder solution be present in an amountof from about 1% to about 3% by weight of the sand.

Other commonly employed additives such as urea and organosilanes can beoptionally used in the binder compositions of this invention. Theorganosilanes, which are known coupling agents, enhance the adhesion ofthe binder to the sand. Examples of useful coupling agents of this typeinclude aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes andureidosilanes.

Other additives which are particularly useful in the practice of thisinvention are phenoxyethanols having the general formula:

    AR--O--CHR.sup.1 --CHR.sup.2 --OH

In this formula, the Ar is the phenyl group or the phenyl groupsubstituted with one or more halogens, hydroxy, alkoxy or alkyl groups.R¹ and R² in the formula may be the same or different and representhydrogen, alkyl or alkoxy.

Exemplary additives include phenoxyethanol, 1-phenoxy-2-propanol,2-(4-bromophenoxy)ethanol and 2-(4-chlorophenoxy)ethanol. Phenoxyethanolis particularly useful additive in the practice of this invention.

The phenoxyethanol additive is used in an amount of at least about 1% byweight of the phenolic resole resin. A preferred concentration is fromabout 2% to about 6% by weight of the phenolic resole resin but greaterconcentrations may be beneficial in some circumstances. The additiveshould be one that in the amount used is soluble in the aqueous alkalinesolution of the phenolic resole resin. These additives have the abilityto increase the tensile strength of cores and molds made with thebinders of this invention as well as those made with conventional resoleresin binders.

When the binders of this invention are used for the production offoundry cores and molds, the refractory material such as foundry sand ismixed thoroughly with the aqueous alkaline binder solution. Mixing iscarried out until substantially all of the sand particles are coatedcompletely and uniformly with the binder solution. The refractorymaterial coated with the binder is then placed in a vented core or moldbox, such as is used in conventional "cold-box" processes.

The mixture of sand and resin is hardened by passing a volatile esterthrough the material in the vented box. The preferred esters used forgassing the mixture are the lower alkyl formates. The most preferredester is methyl formate. As is known in the art, such esters are notusually used as a pure gas, but as a vapor or aerosol in an inertcarrier gas. Such inert carrier gases are those which do not react withthe ester or have an adverse affect on the curing reaction of theproperties of the product. Suitable gases include air, nitrogen orargon.

The following specific examples illustrate the present invention. Theyare not intended to limit the invention in any way. As otherwiseindicated, all parts and percentages are by weight.

EXAMPLE 1

A mixture of 1,000 parts of phenol, 1,276 parts of 50% aqueousformaldehyde solution and 42 parts of a 25% aqueous zinc acetatesolution was heated at 90° C. for 14 hours and then cooled. The freeformaldehyde of the reaction mixture was 8.9%, indicating that about 68%of the formaldehyde had combined with the phenol. Then 850 parts of 45%of potassium hydroxide and 100 parts of water were added. Reaction wascontinued at 80° C. for 100 minutes before the reaction mixture wascooled and 16 grams of gamma-aminopropyltriethoxysilane was added. Theviscosity of the resin was 164 cps at 25° C.

Comparative Test Resin

A comparative test resin was prepared by mixing 1,000 parts of phenol,800 parts of 45% aqueous KOH and 135 parts of water. To this mixture wasadded 1,276 parts of 50% aqueous formaldehyde over a period of 30minutes, while holding the temperature at 80° C. The reaction wascontinued at 80° C. for four hours and then cooled. To this mixture wasadded 16 grams of gamma-aminopropyltriethoxysilane to give a finalproduct which had a viscosity of 154 cps at 25° C.

Tests On Resin Coated Sands

The following tests were performed using the resin of Example 1 and thecomparative test resin. Each resin sample was coated on Wedron 530 sandin a Hobart mixer. The amount of resin used was 1.75% of the weight ofthe sand. The coated sands were then tested making standard AFS (dogbone) tensile cores. Test cores were prepared by blowing the mixture at80 lbs. per square inch (psi) air pressure into a Redford laboratorythree cavity cold box machine. The cores were cured by gassing with a70:30 mixture of methyl formate and air for seven seconds. Tensilestrengths were measured at one minute, 30 minutes, one hour and 24 hoursafter gassing, using a Detroit Testing Machine Company Model CST TensileTester. Results of the tests given in Table I show that cores made usingthe resin of this invention have superior strength to those preparedusing the resins of the prior art:

                  TABLE I                                                         ______________________________________                                        Tensile Strength of Cores Prepared Using Resole Binders                                  Tensile Strength (psi)                                             Resin        1 min.   30 min.  1 hour 24 hours                                ______________________________________                                        Modified Benzylic                                                                          126      110      154    162                                     Ether Resole                                                                  Conventional Resole                                                                        103       94      116    132                                     (Comparative Test)                                                            ______________________________________                                    

EXAMPLE 2

A second series of tests were performed using the resin of Example 1 towhich 4% phenoxyethanol had been added, and the comparative test resinto which 4% phenoxyethanol had been added. The resins were coated on thesand, and the coated sands were tested as described above. The testresults given in Table II show that cores made using the resins of thisinvention have even greater strength when the resins contain theadditive phenoxyethanol. The tests further show that cores made usingthe resins of this invention containing phenoxy ethanol have superiorstrength to those prepared from conventional resole resin containingphenoxyethanol.

                  TABLE II                                                        ______________________________________                                        Tensile Strengths of Cores Prepared Using                                     Resole Binders containing 4% Phenoxyethanol                                              Tensile Strength (psi)                                             Resin        1 min.   30 min.  1 hour 24 hours                                ______________________________________                                        Modified Benzylic                                                                          130      169      172    157                                     Ether Resole                                                                  Conventional Resole                                                                        116      147      167    138                                     (Comparative Test)                                                            ______________________________________                                    

Thus, it is apparent that there has been provided, in accordance withthis invention, a modified benzylic ether resole resin and foundrybinder composition containing this resin that fully satisfies theobjects, aims and advantages set forth above. While the invention hasbeen described in conjunction with specific embodiments thereof, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, it is intended to include all suchalternatives, modifications and variations as set forth within thespirit and broad scope of the appended claims:

What is claimed is: .[.1. A process for preparing a modified benzylicether resole resin comprising the steps: sodium hydroxide and mixturesthereof..].
 15. A binder composition which comprises an aqueous alkalinesolution of a phenolic resole resin, said aqueous solution having asolids content of from about 40% to about 75% by weight, said phenolicresole having an aldehyde:phenol molar ratio of from about 1.2:1 toabout 2.6:1 and an alkali:phenol molar ratio of from about 0.2:1 toabout 1.2:1, wherein the phenolic resole resin is the modified benzylicether resole resin .[.of claim 8.]. .Iadd.obtained by a processcomprising the steps of:(a) first reacting a phenol with a molar excessof an aldehyde in the presence of a divalent metal ion catalyst at a pHbelow 7 until from about 20% to about 90% by weight of the aldehyde hascombined with the phenol; (b) then adding sufficient basic catalyst tothe mixture of step(a) to raise the pH to at least about 8; and (c)heating the mixture obtained in step (b) until the free aldehyde in themixture is less than about 5% by weight of the mixture.Iaddend..
 16. Thebinder composition of claim 15 wherein the aldehyde:phenol molar ratiois from about 1.5:1 to about 2.2:1.
 17. The binder composition of claim15 wherein the alkali used to prepare the aqueous alkaline solution isselected from the group consisting of potassium hydroxide, sodiumhydroxide and mixtures thereof.
 18. The binder composition of claim 17wherein the molar ratio of alkali to phenol is from about 0.4:1 to about0.9:1.
 19. The binder composition of claim 15 which further comprises anadditive in an amount of at least about 1% by weight of the phenolicresole resin, said additive being soluble in the aqueous alkalinesolution and having the general formula:

    Ar--O--CHR.sup.1 --CHR.sup.2 --OH

where Ar=phenyl or phenyl substituted with one or more halogen, hydroxy,alkoxy or alkyl groups and where R¹ and R² may be the same or differentand=hydrogen, alkyl or alkoxy.
 20. The binder composition of claim 19wherein the additive is present in an amount of from about 2% to about6% by weight of the phenolic resole resin.
 21. The binder composition ofclaim 19 wherein the additive is phenoxyethanol.
 22. A foundry moldingcomposition which comprises a granular refractory material, and fromabout 0.5 to about 8% by weight of the refractory material of the bindercomposition of claim
 15. 23. The foundry molding composition of claim 22wherein the granular refractory material is selected from the groupconsisting of silica sand, chromite sand, zircon sand, olivine sand andmixtures thereof.
 24. The foundry molding composition of claim 22wherein the aqueous alkaline solution of a phenolic resole resin ispresent in an amount of about 1% to about 3% by weight of the sand. 25.The foundry molding composition of claim 22 wherein the alkali used toprepare the aqueous alkaline solution is selected from the groupconsisting of potassium hydroxide, sodium hydroxide and mixturesthereof.
 26. The foundry molding composition of claim 25 wherein themolar ratio of alkali to phenol is from about .[.0.4:.]. .Iadd.0.4:1.Iaddend.to about 0.9:1.
 27. The foundry molding composition of claim 22which further comprises a silane.
 28. A foundry molding compositionwhich comprises a granular refractory material, and from about 0.5 toabout 8% by weight of the refractory material of the binder compositionof claim
 19. 29. The foundry molding composition of claim 28 wherein theadditive is present in an amount of from about 2% to about 6% by weightof the phenolic resole resin.
 30. The foundry molding composition ofclaim 28 wherein the additive is phenoxyethanol.
 31. A process for theproduction of foundry cores and molds which comprises:(a) mixing agranular refractory material with from about 0.5% to about 8% by weightof the refractory material of the binder of claim 15; (b) placing themixture of refractory material and binder in a vented core or mold box;and (c) gassing the mixture in the core or mold box with a volatileester.
 32. The process of claim 31 wherein the granular refractorymaterial is selected from the group consisting of silica sand, chromitesand, zircon sand, olivine sand and mixtures thereof.
 33. The process ofclaim 31 wherein the binder is present in an amount of about 1% to about3% by weight of the sand.
 34. The process of claim 31 wherein the alkaliused to prepare the aqueous alkaline solution of binder is selected fromthe group consisting of potassium hydroxide, sodium hydroxide andmixtures thereof.
 5. The process of claim 34 wherein the ratio of alkalito phenol is from about 0.4:1 to about 0.9:1.
 36. The process of claim31 wherein the mixture of refractory material and binder furthercomprises a silane.
 37. The process of claim 31 wherein the volatileester is methyl formate.
 8. A process for the production of foundrycores and molds which comprises:(a) mixing a granular refractorymaterial with from about 0.5% to about 8% by weight of the refractorymaterial of the binder of claim 19; (b) placing the mixture ofrefractory material and binder in a vented core or mold box; and (c)gassing the mixture in the core or mold box with a volatile ester. 39.The process of claim 38 wherein the additive is present in an amount offrom about 2% to about 6% by weight of the phenolic resole resin. 40.The process of claim 38 wherein the additive is phenoxyethanol.